Md. Najib Ibrahim

Speech intelligibility prediction of room with curved surfaces by means of its physical characteristics

In the room, it was found previously that the ear uses the first arriving sound to locate the source, but the early reflections contribute to the intelligibility. Late reflections, on the other hand reduce intelligibility. Therefore, for speech intelligibility a high sound energy fraction is necessary, requiring high early energy and low late energy. Spatial impression which is the subjective effect of early sound reflections that come from the side walls and ceiling, contributes to the sense of envelopment. This paper presents the investigation of speech intelligibility with respect to the physical characteristics of rooms with curved surfaces. The investigated physical characteristics are source‐to‐listener distance (Lr), listener‐to‐the farthest wall (Lwmax), listener‐to‐the closest wall (Lwmin), listener‐to‐the farthest wall and listener‐to‐the average distance to walls (Lwave). In addition to objective acoustics measures such as reverberation time (RT60), early decay time (EDT), average sound absorpt...

Investigation of early‐to‐late sound reflection effect in a room with a dome

The material of a dome is normally very sound reflective. This is due to the fact that the material for inner surfaces of the dome is made of hard material for endurance and easy maintenance. Also, the dome is often situated high above the floor of the room with the intention of providing larger volume and thus creating comfortable envelopment of the dome for people inside it. Due to the height from the floor and the hard material of its inner surfaces, the dome naturally manifests strong sound reflection, sound focusing effects and uneven sound pressure levels. These phenomena also give rise to the reverberation time in a room with a dome. It is the intention of this paper to discuss the effects of early‐to‐late sound reflection with respect to reverberation time and sound reverberant level in a room with a dome.

Investigation of speech intelligibility in building with curved surfaces by means of objective measures

There are two aspects in an acoustics design process that have to be taken care of in order for the room and the sound system to be intelligible. The first is the electronic part of the design. The second is the environment in which the system is to be installed. With the assumptions that the selection of sound system equipment and installation are correct and thorough, the sound reflection pattern and its delay in building with curved surfaces has to be investigated and understood. This paper investigates via measurements as well as through the simulation software the distribution of sound pressure level, sound delay (RT60), time and amplitude of early reflection (Rearly), and late reflection (Rlate) in a symmetrical room and in a room with curved surfaces. Rearly  is categorized as the first‐arriving wave‐front that happens before 35 ms and Rlate is that within 70 and 120 ms. Preliminary investigation has shown that the equal distribution of these objective measures is destroyed with the existence of cu...

Normal‐incidence sound absorption measurement of a perforated panel using a sound‐intensity technique: Theoretical versus experimental

A direct‐piercing carved‐wood panel (DPCWP) is a form of wood carving that allows air to pass through the panel easily. In Malaysia, DPCWPs are available with various perforation ratios, patterns, and elements, and are typically used as part of a wall partition for an enclosed room. It helps in providing natural ventilation, besides it is believed to be able to act as a sound absorber. Circular perforated panels are the simplest form of DPCWP available. It was found out that normal‐incidence sound‐absorption performance of perforated panels can be measured reliably using a sound‐intensity measurement technique. In this paper, normal‐incidence sound‐absorption measurement of a perfortated panel using fixed‐point scanning will be discussed. Close correlations were obtained from 250 Hz to 4 kHz between theoretical and measured sound absorption. Factors contributing toward sound intensity measurement reliability, primarily through its sound quality indicators such as F1, F2, F3, and F4, and the effect of meas...